This application relates to the manufacturing of metal forgings, and, more particularly, to a process for preparing closed-die forgings and removing flashing from the forgings.
Forging is a widely used manufacturing technique for preparing metal articles. In a typical forging operation, a metal forging blank is pressed or pounded into a shape that is close to the preselected final shape. Forging is relatively economical for producing many articles, and additionally produces metal microstructures in the final article that may be beneficial to its performance. Forging is normally accomplished at an elevated temperature, because the strength of the metal is less at higher temperature than at lower temperatures, requiring less power to be expended in the forging operation.
The forging deformation can be accomplished by open die forging, in which the metallic piece is held against an anvil or a flat die and repeatedly struck by a hammer or a forging press. Many large shafts, for example, are prepared by open die forging. Open die forging is usually not intended to produce a highly precise final article.
The other approach to forging is closed die forging, in which two dies are prepared in the form of a negative pattern of the final desired article. The forging blank is placed between the die halves, and they are pressed or hammered together, causing the forging blank to deform to the shape defined by the two dies. In some instances a series of closed dies are used, with the forging blank progressively deformed toward the desired final shape. In many instances, closed die forgings can be made quite precise in shape and dimensions through careful design of dies, forging sequences, and forging conditions such as temperature.
An inevitable result of a closed die forging operation is flashing on the forging. Flashing is a thin layer of metal produced at the interface between the two die halves. It results because the outward flow of the metal under the forging pressure is constrained everywhere but the interface between the dies. The metal naturally extrudes outwardly between the forging dies, leaving the flashing on the sides of an otherwise perfectly formed part.
After forging, the flashing is usually removed from the part by trimming in a shear, grinding with an abrasive, or cutting with a blade, knife, or oxyacetylene torch. Trimming in a shear is relatively fast, but may be difficult to integrate into a high volume production operation due to time and temperature constraints on the shearing operation in relation to the forging operation. Shearing can be imprecise due to the difficulty of aligning the part in the shear, and because of dimensional changes that occur during and after shearing. The misalignment and dimensional changes can result in variable shearing pressures and subsequent shape variations in the part, which is undesirable. Achieving the necessary proper alignment in a shearing operation may be time consuming. Shearing can also cause the portion of the article remaining to be deformed in an unacceptable manner. Tools used in shearing are subject to wear, requiring periodic maintenance and replacement. Finally, shearing cannot be accomplished for some thick flashings, softer metals such as aluminum and unusually shaped forgings. Shearing is also not a reproducible operation because the temperature variations from part-to-part make process controls difficult.
Removal of flashing by grinding is precise, but slow and not practical for many high-volume production operations. Grinding, which is often a manual operation, is dependent upon the skill and care of the operator. Grinding may introduce substantial heat into the part, thereby forming an undesirable heat affected zone with different properties than the rest of the part. Grinding may also result in abrasive particles being embedded in the metal part, which can lead to degradation of the mechanical properties of the part.
There is a need for a technology of high volume forging production in which the removal of flashing is better integrated with the forging operation. The present invention fulfills this need, and further provides related advantages.